1. Field of the Invention
The present invention relates to a method of manufacturing ceramic sintered bodies by means of a hot press method.
2. Description of Related Art
A pressurized sintering method of ceramics by means of a hot press method is generally used for sintering various kinds of ceramics such as silicon nitride, silicon carbide and aluminum nitride. Such a sintering method is applied for manufacture of electric materials such as ferrite for a magnetic head, ferroelectric piezoelectric ceramics, transparent ceramics and transparent piezoelectric ceramics.
The applicant disclosed, in Japanese Patent Laid-Open Publication No. 5-251365 (JP-A-5-251365), a hot pressing of aluminum nitride ceramics to manufacture a substrate for a semiconductor manufacturing apparatus such as a ceramics heater, a ceramics electrostatic chuck, a ceramics high frequency electrode apparatus and a ceramics susceptor. In the method mentioned above, when a formed body made of aluminum nitride powders is accommodated in a hot press apparatus, a graphite foil is arranged between the formed body and a sleeve and between the formed body and a spacer, in order to control the environmental atmosphere of the formed body and also to prevent a reaction between the formed body and the sleeve or the spacer.
In the semiconductor manufacturing apparatus, it is known that a sintered body having a dome shape is used as an electrode for plasma generation by embedding a metal member in the sintered body having a dome shape and conducting electricity through the metal member.
However, in the known hot press method, it is thought to be difficult to obtain a sintered body having an irregular shape other than a planar shape because the shrinkage of the formed body along the pressure applying axial direction is extremely large. On the other hand, the thickness of a ceramic sintered body having an irregular shape is largely varied corresponding to a position on a surface of the ceramic sintered body along a pressure applying axial direction. Therefore, it is thought that pressure is not uniformly applied to various portions of the formed body and the portions are then not uniformly heated.
Therefore, in order to manufacture a sintered body having, for example, a dome shape, a sintered body having a large plane shape is first manufactured by means of the hot press method, and then the thus manufactured sintered body is ground. However, such a grinding step involves a large amount of time. In addition, when a metal member, such as an electrode, is embedded in the sintered body having a plane shape, it is extremely difficult to correctly measure the portion in the sintered body at which the metal member is embedded and grind the sintered body corresponding to the portion of the metal member. Therefore, the drawback is that the embedded position of the metal member is liable to be shifted from a designed normal position.
An object of the present invention is to provide a method of manufacturing ceramic sintered bodies in which a ceramic sintered body having a different thickness along a predetermined axial direction can be obtained.
According to the invention, a method of manufacturing ceramic sintered bodies having a different thickness along a predetermined axial direction, comprises the steps of accommodating a ceramic formed body to be sintered having a different thickness along the predetermined axial direction in a hot press apparatus; setting an upper forming mold and a lower forming mold each having a forming surface corresponding to an upper surface and a lower surface of the ceramic formed body to be sintered, applying a pressure along the predetermined axial direction to the ceramic formed body to be sintered via the upper forming mold and the lower forming mold while heating the ceramic formed body to be sintered to perform a hot press sintering thereof; and controlling a thickness of a ceramic sintered body in such a manner that a maximum thickness in the predetermined direction is not more than two times a minimum thickness in the predetermined direction.
The inventors found that it was possible to sinter the ceramic formed body without generating unevenness of, for example, density at various portions of the sintered body through the use of an upper forming mold and a lower forming mold each having a forming surface corresponding to an upper surface and a lower surface of the ceramic formed body to be sintered. A thickness of the ceramic sintered body is controlled in such a manner that a maximum thickness in the predetermined direction is nor more than two times a minimum thickness in the predetermined direction. Moreover, in the preferred embodiment, the thickness of the ceramic sintered body is continuously varied from the maximum thickness to the minimum thickness.
Here, the use of an upper forming mold and a lower forming mold is a known forming method for axially pressurized forming. However, in the present invention, the upper forming mold and the lower forming mold, each having a forming surface corresponding to an upper surface and a lower surface of the ceramic formed body to be sintered, are used for performing the hot press sintering with respect to the formed body having an irregular shape. In this manner, the properties of the sintered body after hot pressing can be controlled.
In another preferred embodiment, the hot press sintering for the ceramic formed body is performed after the metal member is embedded in the ceramic formed body to be sintered. In this case, the position of the metal member in the sintered body after the hot press sintering can be approximately determined by the position of the metal member just before the hot press sintering. Therefore, it is possible to reduce the positional shift of the metal member in the sintered body as compared with the sintered body obtained according to the known method. Moreover, in this case, it is possible to deform the metal member by embedding the metal member having a planar shape in the formed body and by applying pressure to the metal member via the upper and lower forming molds and further via the ceramic powders in the formed body when the hot press sintering is performed.
In still another preferred embodiment, the metal member is preliminarily formed corresponding to the forming surface of the upper forming mold or the lower forming mold, and the thus formed metal member is embedded in the ceramic formed body to be sintered. In that case, ceramic powders in the ceramic formed body near the metal member after the deformation are moved when the hot press sintering is performed. However, here, since the three-dimensional shape of the metal member corresponds to the forming surface of one of the upper forming mold and the lower forming mold, it is possible to prevent a positional shift of the metal member along the pressurized axial direction, and to further improve the positional precision of the metal member in the sintered body after the hot press sintering.
In still another preferred embodiment, a ceramic sintered body having a dome shape including a projected upper surface and a concaved lower surface, the thickness of which is controlled in such a manner that a maximum thickness in the predetermined direction is not more than Two times a minimum thickness in the predetermined direction, is manufactured by setting a sintering support tool having a cylinder, an upper transcribing forming mold and a lower transcribing forming mold in the hot press apparatus; supplying ceramic raw materials between the upper transcribing forming mold and the lower Transcribing forming mold in the cylinder of the sintering support tool; performing one directional pressing for the ceramic raw materials by means of the upper transcribing forming mold and the lower transcribing forming mold to obtain a first formed body; setting an electrode member on the first formed body; supplying the ceramic raw materials on the first formed body, on which the electrode member is set, in the cylinder of the sintering support tool; and applying a pressure along an axial direction of the sintering support tool to the first formed body, on which the electrode member is set, while heating the first formed body to perform a hot press sintering thereof. In this case, it is possible to manufacture a ceramic sintered body having a dome shape.
In the present invention, as the ceramic formed body to be sintered by means of the hot press sintering, use is made of ceramic powders, formed body of the ceramic powders, cleaned body of the formed body and calcined body of the formed body. Moreover, as a material of the metal member, use is made of a metal or an alloy which is not melted when the hot press sintering is performed.